Estuaries Vol. 14, No. 4, p. 465-480 December 1991 Temporal and Spatial Patterns in Abundance and Diversity of Fish Assemblages in Elkhorn Slough, California zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA MARY M. YOKLAVICH’ GREGOR M. CAILLIET JAMES P. BARRY DAVID A. AMBROSE* BROOKE S. ANTRIM zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCB Moss Landing Marine Laboratories P.O. Box 450 Moss Landing, Calqornia 95039 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIH ABSTRACT: Assemblages of ichthyofauna of shallow inshore habitats along California’s central coast are de- scribed in terms of species composition, abundance, and life-style categories. A total of 22,334 fishes from 65 species and 27 families was collected with otter trawls at six sites in the main channel and tidal creeks of Elkhorn Slough, a tidal embayment and seasonal estuary, and two nearshore ocean stations in Monterey Bay during 44 months between August 1974 and June 1980. G reater than 90% of the catch comprised 10 species. The four dominant species, Cymatogaster aggregata, Leptocottus awnatus, Phanerodon fwcatus, and Embiotoca jacksoni, occurred during most or all seasons and were classified as residents or partial residents. Several abundant species were marine immigrants that seasonally use the slough as spawning and nursery grounds; this resulted in higher abundance and species richness during summer. Species collected during winter largely were slough residents. Species composition and richness varied with distance from the slough entrance. The ocean assemblage was most different, and its similarity to other stations decreased progressively with distance inland and into the tidal creeks. During our study, 5,074 fishes were collected by beach seine in Bennett Slough, a remote shallow marsh basin adjacent to the entrance of Elkhorn Slough. Species richness was relatively low and three euryhaline species accounted for X30% of the total catch. The species assemblage was most similar to those at the tidal creek and most shallow stations of Elkhorn Slough. Resident species numerically dominated assemblages in Bennett Slough and the most inland areas of Elkhorn Slough. The high relative abundance of marine-related fishes (classified as marine, marine immigrant, and partial resident) entering Elkhorn Slough early in life or as spawning adults indicates the importance of this habitat to nearshore fish assemblages. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Introduction zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Shallow bays and estuaries are recognized world- wide as productive habitats used by a variety of fishes for reproduction, feeding, and shelter (Odum and Heald 1975; Dando 1984; Day and Yanez- Arancibia 1985, among others). These systems function as important nursery grounds for larval and juvenile stages of many marine fishes, poten- tially enhancing their early growth and survival (Allen 1982; Rosenberg 1982; Weinstein 1985). This nursery function often has been discussed in terms of the estuarine dependence of marine spe- cies. More broadly, estuarine dependence includes any species using estuaries as essential habitat dur- ing any life history stage (Blaber et al. 1989). Those species regularly entering estuaries to spawn or feed, as well as those completing their entire life cycle in the area, also can be considered to be de- pendent on estuarine systems. Because most species are not dependent entirely on estuaries and are found also in adjacent coastal environments, Lenanton and Potter (1987) sug- gested the term “ estuarine opportunism.” Al- though difficult to evaluate because it requires sea- sonal sampling over several years in all major habitats of the estuary and adjacent marine area, the benefits derived by opportunistic members of the estuarine fish assemblage would be a measure of the interaction between estuarine and coastal marine environments (Darnell and Soniat 1979; Weinstein 198 1). Identifying this inshore-offshore relationship is important to maintaining all coastal resources. 1 Current address: NOAA-Pacific Fisheries Environmental Group, P.O. Box 831, Monterey, California 93942. 2 Current address: NOAA-Southwest Fisheries Science Cen- ter, P.O. Box 27 1, La Jolla, California 92038-027 1. The functional relationship between estuaries and fish communities has been studied widely along the east coast of the United States, particularly in expansive tidal marshes (Shenker and Dean 1979; Q 1991 Estuarine Research Federation 465 0160-8347/91/040485-i 6$01.50/O